How Does Carnitine Support Hashimoto’s?

I can’t believe it’s been over a decade since my Hashimoto’s diagnosis! I have learned so much since that time, and serendipitously continue learning new things about Hashimoto’s, human development, natural medicine, root causes of disease, and recovering from illness, on a daily basis.

I have my clients and readers, family members, my own body, wonderful colleagues, and access to the latest medical research to help!

The more I learn, the more I come back to nutritional deficiencies as root causes of illness. One great example of a root cause known to cause a wide range of symptoms – including fatigue, brain fog, constipation, digestive issues, and muscle weakness and aches – is a deficiency in the nutrient carnitine. People with Hashimoto’s, pregnant/newly postpartum women, and babies (especially preemies) can often be deficient in this important amino acid. ^[1]

I have personally seen people awaken from a brain-foggy “sloth-mode” when they start supplementing with carnitine. I also have a very personal connection – my own postpartum muscle weakness, aches, and pains were reversed with carnitine!

Read on to discover:

• Why our bodies need carnitine
• How carnitine deficiencies occur
• The thyroid, carnitine, and disease connection
• Testing for carnitine deficiency
• The root cause approach to ensuring optimal levels of carnitine

Why Our Bodies Need Carnitine

If you are like a lot of people, you may have never heard of carnitine, but this important nutrient is critical for our body’s ability to optimally burn fat required for energy.

Carnitine is an amino acid that exists in several forms, including acetyl-L-carnitine, L-carnitine, and propionyl-L-carnitine. The Latin word carnus means “flesh.” Eating meat is the primary means for us to take in carnitine through our diet. Our bodies store carnitine in skeletal and cardiac muscle tissues.

Generally speaking, acetyl-L-carnitine (also referred to as ALCAR) is the form that is viewed as most beneficial for the brain; it crosses the blood-brain barrier and has been found in the research to potentially benefit those with various neurodegenerative diseases. ^[2]

L-carnitine is the form that is viewed as being most beneficial to the muscles. In research, it has been shown to resolve muscle weakness and soreness. ^[3] It is often used in supplements intended for athletic performance improvements, optimal fat burning, and muscle recovery.

Propionyl-L-carnitine has been studied for issues relating to circulation, such as high blood pressure or peripheral vascular disease. ^[4]

Research has found that carnitine supplementation supports a reduction in fatigue in hypothyroid patients, as well as improves muscle weakness for both hypo- and hyperthyroid patients. ^[5]

Carnitine provides these health benefits by supporting the health of our mitochondria (powerful energy factories contained within most of our cells), in a number of ways:

• Carnitine transports long-chain fatty acids into the mitochondria where the fatty acids are burned to produce our body’s energy (in the form of adenosine triphosphate – ATP). ^[6]
• Carnitine transports toxic by-products out of our body’s cells (produced during the aforementioned energy production process) so that the toxins don’t accumulate. Mitochondria degradation can occur if too many toxins (also known as free radicals) build-up; this causes slowed energy production, and results in us having less energy. ^[7] It can also cause poor muscle metabolism and other negative health effects.
• As a powerful antioxidant, carnitine counters free radical (oxidative stress) build-up. ^[8] Our mitochondria can be affected by other types of free radical build-up as well. Chronic stress, environmental toxins (such as heavy metals), or a lack of protective antioxidants (like vitamin C), can all affect mitochondria health. ^[9] Carnitine helps minimize this build-up by scavenging for free radicals, and by maintaining and protecting levels of important antioxidant enzymes, such as glutathione peroxidase.

Did you know? Carnitine deficiencies have been associated with thyroid imbalances! Carnitine deficiencies have been found in people with both hyperthyroid as well as hypothyroid conditions. ^[10]

But where does carnitine actually come from?

Let’s talk about how our bodies get carnitine, and why those of us with Hashimoto’s can often be deficient, resulting in symptoms of fatigue, brain fog, muscle weakness, and more.

How Carnitine Deficiencies Occur

Our bodies usually maintain adequate levels of carnitine through three means:

1. Diet: Carnitine is primarily found in animal products, so strict vegans may be deficient in it.

Red/dark meat (beef) is the highest source, followed by pork. Significantly lower amounts are found in fish, chicken, and milk. The average adult diet has been estimated to provide about 75 percent of daily carnitine requirements. Vegetarian diets are also low in lysine and methionine, the two essential amino acids needed to synthesize carnitine.

On top of not taking in enough carnitine through red meat, research has found that the gut microbiota of vegans and vegetarians actually becomes unable to adequately metabolize carnitine. ^[11] Carnitine is one reason why I believe people “recover” from Hashimoto’s on a Paleo-like diet that includes red meat. Many of my clients, readers, and colleagues have reported that red meat consumption (the grass-fed variety of course), seemed to be a key part of their Hashimoto’s recovery.

2. Endogenous biosynthesis: This occurs when the body itself synthesizes additional carnitine. About 25 percent of our carnitine requirement is typically synthesized inside our bodies (from the two amino acids just mentioned: lysine and methionine).

Unfortunately, I have found people with Hashimoto’s may have impairments in their body’s ability to synthesize carnitine due to:

• Multiple nutrient deficiencies (beyond carnitine): Other “cofactors” (additional nutrients needed to support our body in making carnitine) can also be lacking in those with Hashimoto’s, including having adequate amounts of iron (iron deficiency with or without anemia is a common issue for people with Hashimoto’s, and it is thought that low iron may contribute to the low levels of carnitine found in most pregnant women), vitamin B3 (niacin), vitamin B6, and vitamin C. All of these cofactors are needed for the synthesis of adequate levels of carnitine. I see deficiencies in these nutrients in many of my clients, and they are well-known deficiencies in those with Hashimoto’s. Another nutrient that’s crucial for adequate carnitine levels, thyroid health, and energy levels is zinc. ^[12]
• Insufficient stomach acid: This can affect the nutrient absorption of all of the above cofactors, as well as carnitine itself, and low stomach acid is very commonly found with Hashimoto’s.
• The MTHFR gene variation: Not everyone with Hashimoto’s will have this gene variation, but I do find it to be a common culprit relating to nutrient deficiencies and poor detoxification. MTHFR supports methylation, and methylation is crucial for the production of energy, including the synthesis of carnitine. The MTHFR gene variation may also be associated with lower levels of methionine, one of the amino acids needed for the body’s own synthesis of carnitine. ^[13] (This gene variation also impairs the body’s ability to detox heavy metals, further impacting our thyroid hormone levels and energy metabolism, and you can read more about that here.)
• Other root causes of Hashimoto’s: Chronic stress, heavy metal toxicity, and blood sugar imbalances have been shown to negatively affect mitochondrial health. Carnitine supplementation has been found to have positive effects in improving these issues. ^[14]
• Gut infections, including SIBO: Researchers have found that an overgrowth of various bacteria can lead to carnitine deficiency. Interestingly, these overgrowths can be found in conditions as varied as Hashimoto’s, irritable bowel syndrome, restless leg syndrome, and even autism spectrum disorder (ASD). ^[15]

  Gut infections can impact nutrient absorption, metabolism, mitochondrial health, and the immune system. We know, for example, that small intestinal bacterial overgrowth (SIBO) is commonly found with Hashimoto’s (a 2007 study found that about 50 percent of people with hypothyroidism have this infection), and is associated with slow gut motility and intestinal permeability; these in turn can cause nutrient depletions, including iron deficiency (a necessary cofactor for carnitine synthesis). ^[16]Another example can be found in people with ASD having an infection called Clostridia. This infection produces bacterial propionic acid in the gastrointestinal tract. Propionic acid directly impairs the metabolism of carnitine in the body, and also causes a reduction in omega-3-fatty acid levels (which leads to reduced antioxidant capacity and other negative impacts on carnitine reuptake). In clinical studies, many patients with ASD have increased levels of propionic acid in the stool, as well as a history of previous infections; many also have carnitine deficiency. In these populations, supplementing with carnitine has shown improved social and cognitive skills, improved language, and a reduction in behavioral issues. ^[17]

• Epstein-Barr virus (EBV) and other herpes viruses: Epstein-Barr and other herpes viruses, which I have often found as “precursors” to Hashimoto’s and autoimmune disease in my clients’ health timelines, can lead to a depletion of lysine, one of the key amino acids required for the body to produce carnitine. These types of infections impact the immune system and can become triggers for autoimmunity; they can also disrupt ongoing metabolic processes. Research has found that some people do not fully recover from EBV infections and continue to experience ongoing chronic fatigue. In these individuals, there were actual changes found in their gene expression relating to fatty acid metabolism (including carnitine acetyltransferase) and mitochondrial dysfunction. ^[18]
• Impaired reabsorption: There is the natural process by which carnitine is retained and recycled in the body, versus being lost in the urine. Carnitine is reabsorbed by the kidneys, and typically carnitine excretion in urine is low. The exception to that is found, however, in many disease states (including hyper- and hypo-thyroid states), as well as in conditions relating to specific types of diets (high-fat, high-protein, and low-carb). ^[19] Renal reabsorption can also be low in certain health states such as pregnancy, having excess body fat, and chronic fatigue syndrome.

Those with Hashimoto’s (as well as a number of other health conditions) may find that even with the right diet, they have issues that impact their body’s synthesis and retention of healthy levels of carnitine. Let’s look at this connection a bit more closely, and at the other health conditions where carnitine therapy has been investigated.

The Thyroid, Carnitine, and Disease Connection

Because of the importance of mitochondria to our metabolic health, researchers have long looked at carnitine levels in people with a wide variety of metabolic disease conditions, including thyroid disease (both Hashimoto’s and Graves’ disease).

Graves’ Disease

Most of the earliest research (starting in 1959, through early 2000) relating to carnitine and thyroid disease was actually focused on Graves’ disease.

Scientists looking at L-carnitine’s effects on thyroid health suggested that carnitine was a peripheral antagonist of thyroid hormone activity in some tissues (meaning L-carnitine might prevent the entry of T3 and T4 into cells). In hyperthyroidism, with high levels of thyroid hormone, the body was found to burn through and become depleted in carnitine. Higher thyroid hormone levels resulted in higher levels of carnitine being excreted in the urine. ^[20]

Researchers sought to validate earlier laboratory studies relating to carnitine’s effects on improving thyroid hormone levels. In one 6-month study published in 2001, fifty women were given a fixed dose of TSH-suppressive L-T(4) therapy. The women were separated into five groups, with each group getting a different series of carnitine supplementation (2 or 4 g/d oral L-carnitine) or a placebo. Researchers evaluated changes relating to nine thyroid parameters and symptoms. When given either dose of L-carnitine, the women’s thyroid symptoms improved, reversing symptoms of hyperthyroidism. ^[21]

Given this, you may wonder why carnitine would be good for those with hypothyroid issues if carnitine is truly an antagonist for thyroid hormone activity. More recent research has shown that carnitine can be beneficial for both hypothyroidism and hyperthyroidism, with a decreased concentration of carnitine found in the skeletal muscles of people with both thyroid conditions. ^[22]

The action of carnitine appears to play out differently depending on a given individual’s metabolic state and thyroid hormone levels.

Let’s talk more about hypothyroidism and the newer carnitine research. Then, I’ll talk briefly about carnitine research related to a few other health conditions.

Hypothyroidism and Fatigue

In research published in 2016, when hypothyroid patients received levothyroxine, the extra thyroid hormone promoted carnitine synthesis. Yet scientists found that there was still a carnitine deficiency in these patients. Researchers hypothesized that, while the increased thyroid hormone increased carnitine synthesis, it also accelerated mitochondrial fatty acid oxidation (similar to what was seen to happen in a hyperthyroid state), which reduced carnitine levels. So essentially, more was being produced, but also, more was being excreted, resulting in an ongoing deficiency. It turns out that this can cause relative carnitine deficiency, which can result in lingering fatigue (even after thyroid hormone therapy). ^[23]

In the 2016 study, 60 patients who were experiencing hypothyroid-related fatigue, were either given L-carnitine (990 mg L-carnitine twice daily) or a placebo, for 12 weeks. After 12 weeks, the researchers noted that the group receiving L-carnitine did indeed show improvements in fatigue, with the most significant improvements seen in “brain fatigue.” The most significant results were in those younger than 50, those over the age of 50 with high levels of free T3, and those who had hypothyroidism due to a thyroidectomy (who were taking relatively high doses of thyroid hormone). Researchers concluded that these populations were more active metabolically (therefore having relative carnitine deficiency). Other case-based studies have also shown a benefit from L-carnitine on hypothyroid symptoms.

In my own practice, I see fatigue as the main impairment in my clients, even after thyroid hormone treatment improves their thyroid levels. Carnitine supplementation has been a game-changer for many people’s energy levels, brain function, and muscle strength. This has been the case for my clients, as well as for myself.

My experience, as well as current research, mirrors findings relayed in the 2001 Basel Thyroid Study. ^[24] In that study, fatigue was found to be a major symptom in hypothyroidism. Since then, there have been many articles and findings underscoring this point: fatigue can linger on even after a person normalizes their thyroid hormone levels.

Hypothyroidism and Muscle Weakness

Muscle weakness and aching are common in both hyper- and hypothyroidism. Researchers have found that more than half of patients with hypothyroidism had muscle complaints, with 54 percent experiencing muscle weakness and 42 percent experiencing cramps. ^[25]

Why is muscle weakness so common? The metabolic effect of inadequate thyroid hormone is partly to blame. T3 is a huge regulator of mitochondrial health. Reduced triiodothyronine (T3) may cause a reduction in muscle energy metabolism, as well as impact the efficiency of normal muscle function. Thyroxine (T4) deficiency also reduces the body’s ability to make energy.

Research has also shown that, in hypothyroid patients, there was indeed a trend for muscle carnitine content to be lower than normal, and that carnitine levels improved with thyroid hormone treatment. ^[26]

Other research focused on carnitine and muscle weakness seems to support carnitine’s effects relating to muscle integrity. ^[27] For example, research relating to cancer and the use of chemotherapy drugs found that carnitine supplementation was able to help reverse muscle damage and weakness caused by toxic side effects of anticancer drugs. ^[28]

Additionally, a randomized control trial study by Maruyama and colleagues, illustrated that carnitine supplementation helps maintain muscle mass and strength, specifically in individuals undergoing hemodialysis, as well as in those with diabetes and the elderly. ^[29]

The authors randomly placed individuals in two groups, an L-carnitine supplementation group, and a no carnitine supplementation group. They found that individuals within the carnitine supplementation group preserved lean body mass and upper arm strength, while those without supplementation did not.

Combining exercise with an L-carnitine supplement can significantly boost fatty acid oxidation. The boost in fatty acid oxidation allows for more L-carnitine to be taken up into our cells, allowing for increased muscle metabolism and growth.

Carnitine and Other Conditions

In the last few years, my healing repertoire has expanded as I’ve been learning how to heal and reverse numerous conditions, in addition to Hashimoto’s. I’ll be sharing more in future articles and upcoming books, but for this article, let’s talk briefly about the carnitine and metabolic connections seen in other conditions.

Carnitine, Glucose Utilization and Insulin Resistance

I’ve talked a lot in previous articles about how blood sugar imbalances are extremely common in Hashimoto’s. But a fact you may not be aware of is that people with diabetes are up to three times more likely to develop thyroid disease. ^[30] It’s all about each condition’s effect on the body’s metabolism. Insulin resistance and blood sugar imbalance occur in the development of type 2 diabetes, and may be associated with a defect in fatty-acid metabolism in muscle and tissue lipid (fat) accumulation. Low levels of L-carnitine have been found to be associated with diabetic complications. ^[31]

Since L-carnitine has a central role in fat metabolism and has significant antioxidant properties as well, carnitine supplementation has been investigated as a treatment option in the management of type 2 diabetes.

Several animal and human studies have found that L-carnitine supplementation has a beneficial effect on whole body glucose utilization. ^[32] It has also been shown to improve type 2 diabetes markers, such as several lipid parameters, as well as lower oxidative stress. Clinical trials have shown that some carnitine forms, such as ALCAR, reduce pain and vascular-related symptoms in diabetic patients as well. ^[33]

Carnitine and Constipation

A very common symptom that my clients and readers often have is constipation.

Constipation is often rooted in gut motility issues, as well as nutrient deficiencies (magnesium deficiency is a very common one, especially for those with Hashimoto’s).

Think about it: with hypothyroidism, everything slows down, including our body’s ability to move stool through the intestines. Research has found that carnitine deficiency can cause smooth muscle dysmotility (changes in speed, strength, or coordination) of the gastrointestinal tract (similar to what it does to muscle metabolism, causing muscle weakness), which can cause gastrointestinal discomfort and changes in the microbiota (gut dysbiosis), as well as constipation. ^[34]

Research involving different populations of patients suffering from constipation has found that many of them are deficient in carnitine. These deficiencies have been linked to abnormal diets (due to the patients’ condition), medications, and other issues relating to gastrointestinal health (gut motility issues, lack of hydration). In several studies, supplementation with carnitine was shown to improve constipation challenges. ^[35]

One study focused on 27 patients with epilepsy who had motor and intellectual disabilities requiring an enteral nutrition formula diet fed via tubes (known to contain less carnitine), and who had also been prescribed valproate sodium (an anti-epileptic drug). It was found that they had severe constipation as well as carnitine deficiency. ^[36]

Researchers determined this was likely due to their abnormal diet (which included low levels of carnitine), as well as valproate sodium’s known side effects. In the study, each of the patients’ level of existing carnitine was correlated with the degree of constipation they were experiencing.

Carnitine supplementation with 10-50 mg/kg/day significantly reduced symptoms of constipation.

In another small study involving 15 patients receiving hemodialysis (where blood is pumped out of the body to an artificial kidney machine), they were found to have gastrointestinal symptoms, including constipation (likely due to restrictions in their water intake required as part of their therapy), as well as carnitine deficiency. Supplementation with L-carnitine tablets (900 mg) for three months, increased total carnitine levels and improved their constipation, as well as other gastrointestinal symptoms. ^[37]

As a first-line defense against constipation, I will usually recommend adding more fiber to one’s diet and taking magnesium supplements. But if someone has other symptoms such as fatigue, muscle weakness, and brain fog, or symptoms of low iron such as hair loss (low iron is associated with carnitine deficiency), I will often test for carnitine levels and suggest dietary adjustments or supplements. Supplementation of L-carnitine has been shown to improve discomforts associated with gastrointestinal disorders and the microbiota, including constipation.

Carnitine and The Gut-Brain Connection

The research (and my own experience with clients) tells us that people with Hashimoto’s will typically have some form of intestinal permeability (“leaky gut”), along with having a genetic predisposition and one or more triggers. ^[38] Common triggers for leaky gut include stress, food sensitivities, nutrient deficiencies, toxins, medications, etc. Gut bacteria balance can also be affected by gut infections such as H. pylori, Blastocystis hominis, yeast overgrowth, reactivated Epstein-Barr virus, and small intestinal bacterial overgrowth (SIBO).

More and more, researchers are discovering that the microbes that control our digestive system can also control our neurobiology, or the gut-brain neuroendocrine metabolic axis. ^[39] What this means is that, disruptions that occur to the gut (for instance, from taking an antibiotic, taking acid-suppressing medications for acid reflux, or eating an inflammatory food like gluten), can upset the microbiome, cause intestinal permeability (leaky gut), and result in a shared gut-brain inflammatory event.

The type of gut-brain connection (gut bacterial overgrowth resulting in brain fog and fatigue) seen with Klebsiella is very common with autoimmune conditions. What happens in the gut can affect the body’s overall metabolism, mitochondrial health, immune system, hormone balance, and even brain health.

These events can further affect nutrient absorption and gut motility, and become a vicious cycle causing symptoms such as constipation and muscle weakness, as well as neurological issues such as mood swings, fatigue, brain fog, etc.

Think about the example mentioned earlier relating to autism and carnitine deficiencies: the outcome of something like a gut infection or antibiotic use, can alter intestinal bacterial populations (in this case, increased propionic acid causing a carnitine deficiency). Even though this issue is gut-related, carnitine supplementation was shown to actually help improve brain function (social and cognitive skills) in this particular population of patients. ^[40]

So remember what I – and other functional practitioners – always say, “All disease (and thereby all healing) begins in the gut.” Should you want to learn more about this topic, I encourage you to check out my article on the importance of gut health in Hashimoto’s.

Carnitine, Healthy Weight Management, and Athletic Performance

Carnitine has been a supplement of interest to athletes for some time, associated with the preservation of lean body mass, increased skeletal muscle, increased fat burning, and enhanced exercise performance and muscle recovery. It may be especially helpful for people consuming a low-carb diet. ^[41] Many of my clients come to my practice struggling to lose weight. Just like with blood sugar imbalance, the ability to lose weight is very much tied to our metabolism and other root causes that can trigger autoimmune symptoms.

Carnitine and Fertility

Since mitochondrial metabolism provides energy to cells – including reproductive cells – it makes sense that carnitine could prove beneficial as a potential treatment for infertility. ^[42]

Fertility challenges are a common issue associated with thyroid disease. ^[43] Hypothyroidism has been associated with altered ovulatory function, subfertility (the inability to conceive), menstrual irregularities, and higher miscarriage rates. ^[44] In females, both L-carnitine and ALCAR have been shown to improve female fertility. L-carnitine has been shown to improve energy supply to cells and provide superior antioxidant support affecting female reproduction; ALCAR, too, has been shown to provide antioxidant support for female fertility. ^[45]

One study illustrated that supplementing IVF treatment with L-carnitine can improve fertility outcomes. ^[46] The authors found that after supplementing L-carnitine while on IVF treatment, women who were not able to conceive before, became pregnant and gave birth to healthy neonates. The authors explained that L-carnitine helped in improving embryo quality and supported the healthy development of the egg after insemination.

In males, L-carnitine produces energy necessary for improved sperm respiration and motility, and may improve upon the negative effects of free radical-induced oxidative stress. ^[47]

I happened to be taking L-carnitine before I became pregnant with Dimitry, and I believe that helped to get my body nourished well enough to conceive.

When I was finishing up Hashimoto’s Protocol and the Thyroid Secret, I was under a lot of deadlines! (Yikes.) I ended up having some new symptoms (and a resurgence of some old symptoms) come up, including body aches, fatigue, and brain fog. I ended up doing some of my recommended testing on myself, including the GI-MAP test.

The test revealed an overgrowth of Klebsiella bacteria in my gut. Klebsiella can lead to an excess of ammonia, which has been tied to brain fog, fatigue, and body aches. ^[48] In addition to following a Klebsiella protocol, I also started on carnitine to help with clearing out ammonia. Interestingly, this infection has also been connected to ankylosing spondylitis, an autoimmune condition that causes pain and fatigue. I am wondering, had I not known what I know, if I would now have this additional diagnosis.

Carnitine and Endometriosis

I recently received a question from a reader about the connection between endometriosis and carnitine. I looked deeper into this connection and there is some conflicting information, so I reached out to my friend Jessica Drummond, who specializes in women’s health, to get some further insight into whether or not carnitine may be helpful for those with endometriosis.

L-carnitine may be helpful for women with endometriosis because of its role as an antioxidant, particularly when it comes to fertility. A 2016 study showed that the combination of N-acetyl cysteine (NAC), another antioxidant, and L-carnitine, was able to prevent damage to the eggs of women with mild endometriosis, suggesting it may be able to boost fertility and improve outcomes of in vitro fertilization (IVF) in women with mild endometriosis. ^[49] Other studies found that it may improve fertility through its effects on cellular stress and through enhanced energy production in reproductive cells. ^[50]

It’s important to note that recent research has suggested that a Fusobacterium infection may actually be at the root of endometriosis. ^[51] Carnitine has been shown to actually feed some pathogenic bacteria in the gut, and it appears that through its effects on TMAO production, it can feed Fusobacterium. ^[52] TMAO is a metabolite produced by gut bacteria, and high levels have been linked to a variety of cardiovascular diseases. ^[53]

That being said, if a Fusobacterium infection is at the root cause of your endometriosis, carnitine may actually make it worse! While short-term, it may be wise to restrict TMAO-feeding substances such as carnitine and choline, this would obviously not be curative. In contrast, using targeted treatments for Fusobacterium, such as metronidazole or berberine, would be the recommended root cause approach. ^[54] If you have endometriosis, I would suggest gut testing and addressing any pathogenic overgrowths or infections before attempting to supplement with carnitine.

Carnitine and Pregnancy

At a certain point in my pregnancy, I developed what my hubby and I playfully called a “burger deficiency.” I would be tearful and exhausted unless I had exactly two burgers a day. I vaguely remember telling my husband, Michael, that I didn’t feel loved one day, because he hadn’t gotten me my grass-fed burgers. It may have been snowing and 5 pm, and he may have had to brave the snow and traffic to fetch said burgers, but I digress. 🙂

Pregnant women are known to have multiple deficiencies and are often touted for intuitively craving whatever they are deficient in. I happened to be deficient in iron (per lab testing), and, of course, red meat is a rich source of iron… But also, each burger contained roughly 500 mg of carnitine. 😉 I had already been taking 500-1000 mg of carnitine per day (500 mg has been the studied dose in pregnancy research I have seen), but perhaps 2000 mg may have been a more appropriate amount to take due to my history of Hashimoto’s, and because I had to increase thyroid hormones while pregnant.

While I never had my carnitine levels tested, I felt so much better after eating my burgers… After having my son, I stopped eating my burger-enriched diet. I ended up feeling weak and had so much muscle pain and muscle loss that I found my yoga class unbearable. I eventually started taking carnitine again and within days, my muscle pain and weakness resolved, and my muscle strength started building up again!

Research has suggested that low iron levels may be the underlying factor in decreased carnitine levels during pregnancy (as iron is a needed cofactor in the synthesis of carnitine in the body). ^[55] One 2009 study with 26 pregnant women found that those taking 500 mg of L-carnitine during pregnancy, starting at week 13 of gestation through birth, normalized their levels of carnitine. ^[56] (Meanwhile, the placebo group showed continued reductions in their plasma carnitine levels.)

There was a positive correlation between iron status and plasma carnitine. Researchers suggested that low levels of iron reduced the rate of carnitine production.

That said, one 2010 study did not find sufficient data to conclude that insufficient iron status was the primary reason for the low plasma carnitine levels observed in pregnant women. ^[57] They found that the cause was likely a low availability of precursors of carnitine biosynthesis (specifically, trimethyllysine and gamma-butyrobetaine, associated with the amino acid lysine and its role in the synthesis of carnitine).

Whatever the reason (it may turn out to be multiple reasons, of course), it is important to make note of the fact that during pregnancy, the mother’s plasma carnitine levels are subject to greatly decrease. It has been estimated that by the time of delivery, plasma carnitine concentrations may decrease to about half of that of non-pregnant women. So, burgers (and carnitine supplementation) are recommended. Bring on the burgers!

Carnitine and Premature Infants

Just like the research connecting nutrient deficiencies (such as carnitine) to developmental delays and low muscle tone, there has been research focused on carnitine supplementation effects on preemies (premature babies).

Carnitine is transferred across the placenta, primarily during the third trimester, so preterm infants often develop carnitine deficiencies. Breast milk and infant formulas contain carnitine, but parenteral nutrition that preemies often get (through an IV) does not routinely contain carnitine. ^[58]

In one 2006 study, 29 premature newborns were split into control and placebo groups, and studied for up to eight weeks. ^[59] The control group was given carnitine supplementation at 20 mg/kg/day, which resulted in increased plasma concentrations of total carnitine. More exciting still, carnitine supplementation had a positive effect on catch-up growth, with the infants regaining their birth weight more rapidly than the placebo group (without carnitine supplementation).

Though there is some conflicting research on this topic, given the other potential health benefits and safety profile of carnitine, a woman might want to discuss the use of carnitine with her doctor as a treatment option should she have a preterm infant.

Carnitine and Developmental Delays

Having a little boy, I am always fascinated by how our body can grow, heal and thrive or struggle — due to our environment. In studying early childhood development to ensure my son was properly nourished, I came across research connecting gross-motor delays and low muscle tone in children, to carnitine deficiency. ^[60]

Low muscle tone (hypotonia) can be a sign of many underlying conditions, including vitamin deficiencies (B1 and other B vitamins), hypothyroidism, carnitine deficiency, creatine deficiency, and methylation issues, as well as genetic conditions (of which there are hundreds).

Nutrient deficiencies in particular can be caused by malabsorption issues, bacterial overgrowth (SIBO, Candida), slow gut motility, diet, toxin exposures, etc. Many of these issues can actually be related to others; for example, a poor diet can cause slow gut motility, which can negatively impact nutrient absorption, which can further impact muscle tone and create a vicious cycle.

One case study found that an infant with delayed development had slow gut motility along with other gastrointestinal symptoms, such as infrequent bowel movements, and was found to have low levels of carnitine. ^[61] The culprit turned out to be a soy-based liquid diet deficient in carnitine, which was resolved with carnitine supplementation.

The important takeaway is for you to have your child evaluated should you notice signs of low muscle tone. Symptoms can include: your child’s head or body becoming more flexible and floppy, lingering fatigue, poor gross motor tasks, a preference to be sedentary, and feeding difficulties. Most pediatricians will ask questions relating to these types of symptoms, but you may need to advocate for a root cause approach, such as evaluating possible nutrient deficiencies including carnitine, if your child is found to be experiencing low muscle tone.

A Possible Link Between Carnitine and Autism

Earlier, I mentioned how gut infections and bacterial imbalances can result in carnitine deficiencies in those with autism spectrum disorder (ASD). There have also been specific genetic linkages found involving carnitine deficiency and autism.

Metabolic disorders are very inheritable, and researchers have identified genetic variations on genes involved with carnitine production, among other things. ^[62] L-carnitine may be lower in some patients with ASD (one study estimated this at 10-20 percent), due to an inability to make or transport carnitine. ^[63] In limited research, L-carnitine supplementation has seemed to improve symptoms of autism in some patients. ^[64]

One example of a specific genetic variation linking carnitine deficiency and autism is the TMLHE gene mutation. This gene variation negatively impacts carnitine transport across the blood-brain barrier (in males and not females), preventing the synthesis of a carnitine precursor called trimethyllysine. This genetic variation is estimated to affect 1 in 350 males in the United States.

Of these males, about 3 percent develop autism (note that less than 1 percent of all autistic males with autism have the TMLHE mutation, so it is clearly just one of many possible genetic associations). ^[65]

This nutrient deficiency/disease correlation, however, has been hypothesized to reveal a risk factor for autism that could potentially be addressed through early intervention in infant nutrition.

For this particular population of boys, could a viable preventative strategy be simply to ensure carnitine is provided in the diet as an infant goes from carnitine-rich milk as their primary food, to juices, fruits, and other foods containing reduced amounts of carnitine?

Here is an interesting video that discusses this nutritional intervention hypothesis for this specific population.

In a case study of a young male ASD patient with this same genetic variation, carnitine supplementation was found to resolve his neurodevelopmental regression. ^[66]

It is gratifying to think that such simple nutritional interventions could make such an amazing difference to a child — and family’s — life. More research is needed to further address these types of connections and treatment recommendations.

Note that a particular prescription drug for epilepsy control, Depakote (generic: valproic acid), has been found in research to be associated with a significantly increased risk of autism in offspring, when used by mothers during pregnancy. ^[67] This drug has also been shown to result in carnitine deficiencies in a number of studies involving children. ^[68] I first learned about this connection in my early days as a consulting pharmacist, working with people with developmental disabilities who had used various medications for epilepsy. Our team occasionally recommended carnitine for people on valproic acid/Depakote, to help with residual side effects like muscle weakness and constipation. We sometimes had clients with severe bowel impactions, and I wonder if carnitine deficiency was at the root of this.

Other Disease Investigations Relating to Carnitine

Carnitine supplementation has been used in patients with cardiovascular pathologies, including peripheral vascular disease, muscular hypoxia, angina, congestive heart failure, and hemodialysis.

Additionally, carnitine has shown protective properties against hypertension, hyperlipidemia, hyperglycemia, diabetic ketoacidosis, insulin resistance, insulin-dependent diabetes mellitus, obesity, and other conditions that enhance cardiovascular pathology. ^[69]

Having a deficiency in carnitine may impact many areas of your body. But what would a conventional medicine doctor likely do if you come to them complaining of fatigue, brain fog, digestive issues, and/or muscle weakness?

Testing for Carnitine Deficiency

When experiencing symptoms such as fatigue, brain fog, and muscle weakness, a simple blood test can be done to check the levels of carnitine in the blood. While it’s always better to work with a good functional practitioner for interpretation, you can order a wide variety of helpful labs yourself. I often recommend Ulta Lab Tests, because you can self-order the tests and later submit the charges to your insurance for possible reimbursement (different insurance plans may or may not cover this, so always check with yours).

When checking your carnitine levels, you could also check another common marker that points to developing carnitine deficiencies, which is having low ferritin (stored iron) levels. This can be especially helpful if you are experiencing specific (and maddening!) symptoms of low ferritin, like hair loss. Remember that iron is a cofactor nutrient that the body needs to manufacture carnitine. The two tests I like are the Ulta Lab Carnitine test and Ulta Lab Ferritin test. Should you find that you are low in ferritin (due to iron deficiency or possibly iron anemia), it is important to address that root cause as well.

You can also test your creatine kinase (CK) levels. The Ulta Lab Creatine Kinase test is an inexpensive test used by functional medical practitioners. While there are various causes for this enzyme to be elevated, muscle damage, or a problem with thyroid hormones, are two potential causes. ^[70]

It turns out that this test can often uncover a thyroid issue much earlier than the typical thyroid test (for TSH levels alone) will! This is so important to know!

The Root Cause Approach to Ensuring Optimal Levels of Carnitine

If you’ve already been diagnosed and are taking thyroid hormone therapy — yet are still suffering from fatigue, muscle weakness, or other symptoms — it’s time to look at common triggers for your symptoms, including focusing in on nutrient deficiencies such as carnitine and its cofactors (as mentioned earlier in this article).

Optimal carnitine levels can help ensure you are supporting your mitochondria and metabolism. This may, in turn, address fatigue, brain fog, and muscle aches. Here are some initial things I’d look at and recommend.

1. Include carnitine in your diet.

The easiest place to start is by ensuring you are including good, clean sources of carnitine in your diet, like quality, hormone/antibiotic-free, organic meats. I feel that most of us actually have to push ourselves to eat less red meat, so this isn’t likely a big problem. I think our bodies actually crave meat when they need more nutrients such as carnitine. Remember, when I was pregnant, I craved burgers! (Dr. Ben Lynch actually recommends carnitine supplementation to be given during pregnancy.) If you are vegetarian, your best option for a food-based source of carnitine is dairy products, though they contain much less carnitine than animal proteins.

2. Address low stomach acid to ensure optimal nutrient absorption.

Remember when we talked about the causes of fatigue and muscle weakness, and how one root cause — nutrient depletions — was affected by low stomach acid? I find that this is a common issue in people with Hashimoto’s and can affect the absorption of many vital nutrients.

I recommend reviewing my article on low stomach acid — and if you think you might have low stomach acid, try the recommended Rootcology supplement, Betaine with Pepsin (this was a game-changer for me!). Sufficient stomach acid for nutrient absorption will help ensure that vital nutrients such as carnitine, iron, zinc, and B-vitamins are readily absorbed.

3. Address low iron levels.

As I mentioned earlier, iron is a cofactor for the biosynthesis of carnitine in our bodies, and I find that low levels of iron (with or without anemia) can greatly affect fatigue and many other symptoms (such as hair loss, a problem I had for many years). Diet is a factor here (with meat once again being the best source).

Many of my clients find that bumping up their vitamin C intake helps with iron absorption. For additional recommendations relating to low iron and iron anemia, including testing you can do, please review this article on common nutrient deficiencies.

4. Optimize your carnitine levels!

I created a targeted supplement to help the body meet its carnitine requirements (to support your mitochondria, your brain and muscle metabolism, as well as help improve upon glucose tolerance).

Rootcology’s Carnitine Blend uniquely combines L-carnitine and acetyl-L-carnitine into one convenient 500 mg capsule. (The recommended dose for hypothyroidism in the 2016 study referenced earlier was 1800 mg per day. Remember that some 75 percent of the usual carnitine intake comes from diet, and about 25 percent comes from the body’s own synthesis.)

This blend works to increase carnitine levels in the body (supporting your mitochondrial health); additionally, each form may have its own specific benefits. L-carnitine has been reported to resolve Hashimoto’s-related fatigue and works to support antioxidant activities in the body.

Acetyl-L-carnitine has unique brain-supportive properties and may help to reduce mental fatigue (bye-bye brain fog!). (58)

You have nothing to lose, because my Rootcology product offers a 30-day, 100% satisfaction guarantee! If you are unsatisfied for any reason, you may return the product within 30 days for a full refund, minus shipping/handling fees.

Here’s what Debbie L. had to say about Rootcology Carnitine Blend:

“I purchased Carnitine about 2 months ago and have been thrilled! I play tennis daily and as a result I’m told I needed knee/shoulder surgeries. I’ve put it off, changed my diet and added this supplement and my joints don’t hurt anymore. I don’t feel 25yrs older than I am anymore. I’m not sluggish and the weight is slowly coming off. I’ve followed Dr Wentz for a long time and I don’t know why I waiting so long to order this!! Thank you!”

Precautions

Warning: Not to be used with peripheral vascular disease, high blood pressure, liver disease due to alcoholism (cirrhosis), diabetes, kidney disease, or a history of seizures.

Consult your practitioner before supplementing if you are taking AZT, doxorubicin, isotretinoin (Accutane), valproic acid (Depakote), or blood thinning medications.

A note on thyroid hormones: Carnitine has traditionally been used by individuals with hyperthyroidism to help with symptoms resulting from hyperthyroid-induced carnitine depletion (such as muscle wasting), so scientists initially believed that carnitine acted like an “antagonist” or a thyroid hormone receptor blocker, and cautioned against using carnitine in hypothyroidism.

However, subsequent research has shown that carnitine acts to modulate thyroid hormones within our cells, so it can act like an “agonist” (a substance that initiates a response when combined with a receptor) helping thyroid hormone action in cases of hypothyroidism, and as an “antagonist” (blocker) in cases of hyperthyroidism. Studies have shown benefits in both hypothyroidism and hyperthyroidism.^[71]

As a best practice with all interventions used for Hashimoto’s, I recommend tracking symptoms, testing thyroid hormone levels, and testing thyroid antibodies after starting new therapies.

Thyroid medications are goldilocks hormones, which means they need to be used in just the right dose — and there are risk factors of being overmedicated.

I recommend testing thyroid hormone levels every six to 12 weeks while using complementary therapies, including root cause medicine, diet, or supplements that may optimize your thyroid function, improve the absorption of thyroid medications, and/or reduce your requirement for thyroid medications (you know, all the stuff I recommend on my website!), as well as when incorporating new lifestyle changes, to ensure your thyroid medication dosage is optimized – or sooner, if you are showing any of the above-mentioned symptoms.

Symptoms of overmedication include, but are not limited to: rapid or irregular heartbeat, nervousness, irritability or mood swings, muscle weakness or tremors, diarrhea, menstrual irregularities, hair loss, weight loss, insomnia, chest pain, and excessive sweating. Do not start, change, increase, decrease or discontinue your medications without consulting with your physician.

Next Steps to Feeling Better

If you are experiencing symptoms such as fatigue, brain fog, constipation, muscle weakness and aches, and digestive issues — even after starting thyroid hormone treatment — it can be due to a single root cause, such as a deficiency in carnitine. The good news is that tackling this single root cause can help resolve a number of your nagging, lingering symptoms.

I always suggest people work with a knowledgeable functional medicine practitioner to get started on their healing journey. If you don’t currently have a good functionally inclined practitioner, I highly recommend that you check out my list. Functional medicine practitioners will work to ensure an early diagnosis of your thyroid condition, and will then optimize thyroid medications (to achieve optimal versus “normal” TSH levels).

They will not just look at individual symptoms, but will look at your symptoms as a whole, as well as your health history timeline, in order to find clues as to the root cause issues that may be affecting you.

They will also likely look at underlying (and common thyroid) issues, such as nutrient depletion and absorption issues that a conventional medicine doctor might not look at, and whether you have the MTHFR gene variation (which can impair thyroid hormone levels and energy metabolism).

While searching for a practitioner, you can still make progress yourself! Diet is an easy place to start, along with assessing whether you may suffer from low stomach acid or one of the aforementioned (and very common) nutrient deficiencies. My Rootcology Carnitine Blend is also something you can try yourself. Carnitine is a very well-tolerated amino acid that the body loves.

I provide many protocols and recommendations throughout my blog as well as in my book, Hashimoto’s Protocol.

P.S. I love interacting with my readers on social media, and I encourage you to join my Facebook, Instagram, TikTok, and Pinterest community pages to stay on top of thyroid health updates and meet others who are following similar health journeys. For recipes, a FREE Thyroid Diet start guide, notifications about upcoming events, and the Nutrient Depletions and Digestion chapter from my first book for free, be sure to sign up for my email list!

My mission is to help you along your Hashimoto’s journey, and to share all of the fascinating emerging research in order to help you feel better. Please let me know if you have questions, and don’t forget to share your successes with the rest of our community!

References

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^[2] National Institutes of Health. Carnitine: What Is It? Updated October 10, 2017. Accessed May 11, 2022. https://ods.od.nih.gov/factsheets/Carnitine-HealthProfessional/#en27; Marcon M, Mocelin R, de Oliveira DL, et al.. Acetyl-L-carnitine as a putative candidate for the treatment of stress-related psychiatric disorders: Novel evidence from a zebrafish model. Neuropharmacology. 2019 May 15;150:145-152.
^[3] Sinclair C, Gilchrist J, Hennessey J, et al. Muscle carnitine in hypo- and hyperthyroidism. Muscle & Nerve. 2005. 32. 357-9. https://www.researchgate.net/publication/7933618_Muscle_carnitine_in_hypo- _and_hyperthyroidism; Maruyama T, Maruyama N, Higuchi T, et al. Efficacy of L-carnitine supplementation for improving lean body mass and physical function in patients on hemodialysis: a randomized controlled trial. Eur J Clin Nutr. 2019;73(2):293-301. doi:10.1038/s41430-018-0348-y; Fielding R, Riede L, Lugo JP, Bellamine A. l-Carnitine Supplementation in Recovery after Exercise [published correction appears in Nutrients. 2018 Apr 26;10(5):]. Nutrients. 2018;10(3):349. Published 2018 Mar 13. doi:10.3390/nu10030349
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^[5] Benvenga S, Feldt-Rasmussen U, Bonofiglio D, et al. Nutraceutical supplements in the thyroid setting: health benefits beyond basic nutrition. Nutrients. 2019 Sep 13;11(9). pii: E2214.; An JH, Kim YJ, Kim KJ, et al. L-carnitine supplementation for the management of fatigue in patients with hypothyroidism on levothyroxine treatment: a randomized, double-blind, placebo-controlled trial. Endocr J. 2016 Oct 29;63(10):885-895. Epub 2016 Jul 16. https://www.researchgate.net/publication/7933618_Muscle_ carnitine_in_hypo-_and_hyperthyroidism; Benvenga S, Ruggeri RM, Russo A, Lapa D, Campenni A, Trimarchi F. Usefulness of L-carnitine, a naturally occurring peripheral antagonist of thyroid hormone action, in iatrogenic hyperthyroidism: a randomized, double-blind, placebo-controlled clinical trial. J Clin Endocrinol Metab. 2001 Aug;86(8):3579-94.; Fariduddin MM, Bansal N. Hypothyroid Myopathy. [Updated 2019 May 5]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2019 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK519513/
^[6] Longo N, Frigeni M, Pasquali M. Carnitine transport and fatty acid oxidation. Biochim Biophys Acta. 2016 Oct;1863(10):2422-35; Semba RD, Trehan I, Li X, et al. Environmental enteric dysfunction is associated with carnitine deficiency and altered fatty acid oxidation. EBioMedicine. 2017 Mar;17:57-66.
^[7] Sharma S, Black SM. Carnitine homeostasis, mitochondrial function and cardiovascular disease. Drug Discov Today Dis Mech. 2009;6(1-4):e31-e39.; Picard M, McEwen BS. Psychological stress and mitochondria: a conceptual framework. Psychosom Med. 2018 Feb/Mar;80(2):126-140.
^[8] Ibid
^[9] El-Sherbini ES, El-Sayed G, El Shotory R, et al. Ameliorative effects of l-carnitine on rats raised on a diet supplemented with lead acetate. Saudi J Biol Sci. 2017 Sep;24(6):1410-1417.; Covarrubias-Pinto A, Acuña AI, Beltrán FA, et al. Old things new view: ascorbic acid protects the brain in neurodegenerative disorders. Int J Mol Sci. 2015 Nov 27;16(12):28194-217.
^[10] Benvenga S, Feldt-Rasmussen U, Bonofiglio D, et al. Nutraceutical supplements in the thyroid setting: health benefits beyond basic nutrition. Nutrients. 2019 Sep 13;11(9). pii: E2214.; An JH, Kim YJ, Kim KJ, et al. L-carnitine supplementation for the management of fatigue in patients with hypothyroidism on levothyroxine treatment: a randomized, double-blind, placebo-controlled trial. Endocr J. 2016 Oct 29;63(10):885-895. Epub 2016 Jul 16. https://www.researchgate.net/publication/7933618_Muscle_ carnitine_in_hypo-_and_hyperthyroidism; Benvenga S, Ruggeri RM, Russo A, Lapa D, Campenni A, Trimarchi F. Usefulness of L-carnitine, a naturally occurring peripheral antagonist of thyroid hormone action, in iatrogenic hyperthyroidism: a randomized, double-blind, placebo-controlled clinical trial. J Clin Endocrinol Metab. 2001 Aug;86(8):3579-94.; Fariduddin MM, Bansal N. Hypothyroid Myopathy. [Updated 2019 May 5]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2019 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK519513/
^[11] Karlsson F, Tremaroli V, Nielsen J, Bäckhed F. Assessing the human gut microbiota in metabolic diseases. Diabetes. 2013 Oct;62(10):3341-9.; Fröhlich E, Wahl R. Microbiota and thyroid interaction in health and disease. Trends Endocrinol Metab. 2019 Aug;30(8):479-490.
^[12] Silena Barton-Wechsler, David L Stachura, Emily Ho, et al. Effects of zinc supplementation on Carnitine and lactate concentrations in cultured liver cells. The FASEB Journal. 2017 31:1_supplement, 802.5-802.5
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^[14] Picard M, McEwen BS. Psychological stress and mitochondria: a conceptual framework. Psychosom Med. 2018 Feb/Mar;80(2):126-140.; Sun Q, Li Y, Shi L, et al. Heavy metals induced mitochondrial dysfunction in animals: Molecular mechanism of toxicity. Toxicology. 2022;469:153136. doi:10.1016/j.tox.2022.153136; Fujimaki S, Kuwabara T. Diabetes-Induced Dysfunction of Mitochondria and Stem Cells in Skeletal Muscle and the Nervous System. Int J Mol Sci. 2017;18(10):2147. Published 2017 Oct 14. doi:10.3390/ijms18102147
^[15] Obrenovich MEM. Leaky gut, leaky brain? Microorganisms. 2018 Oct 18;6(4). pii:E107.; Demarquoy C, Demarquoy J. Autism and carnitine: A possible link. World J Biol Chem. 2019;10(1):7–16.; Christensen J, Grønborg TK, Sørensen MJ, et al. Prenatal valproate exposure and risk of autism spectrum disorders and childhood autism. JAMA. 2013 Apr 24;309(16):1696-703.; Macfabe D. Autism: metabolism, mitochondria, and the microbiome. Glob Adv Health Med. 2013;2(6):52–66.; Carnitine. Treat Autism. Published October 8, 2012. Accessed June 16, 2020. http://treatautism.ca/2017/10/08/carnitine/; Ziats MN, Comeaux MS, Yang Y, et al. Improvement of regressive autism symptoms in a child with TMLHE deficiency following carnitine supplementation. Am J Med Genet A. 2015 Sep;167A(9):2162-7.
^[16] Lauritano E, Bilotta A, Gabrielli M et al. Association between Hypothyroidism and Small Intestinal Bacterial Overgrowth. The Journal of Clinical Endocrinology & Metabolism. 2007;92(11):4180-4184. doi:10.1210/jc.2007-0606.
^[17] Demarquoy C, Demarquoy J. Autism and carnitine: A possible link. World J Biol Chem. 2019;10(1):7–16.; Christensen J, Grønborg TK, Sørensen MJ, et al. Prenatal valproate exposure and risk of autism spectrum disorders and childhood autism. JAMA. 2013 Apr 24;309(16):1696-703.; Macfabe D. Autism: metabolism, mitochondria, and the microbiome. Glob Adv Health Med. 2013;2(6):52–66.; Carnitine. Treat Autism. Published October 8, 2012. Accessed June 16, 2020. http://treatautism.ca/2017/10/08/carnitine/; Ziats MN, Comeaux MS, Yang Y, et al. Improvement of regressive autism symptoms in a child with TMLHE deficiency following carnitine supplementation. Am J Med Genet A. 2015 Sep;167A(9):2162-7.
^[18] Vernon SD, Whistler T, Cameron B, et al. Preliminary evidence of mitochondrial dysfunction associated with post-infective fatigue after acute infection with Epstein Barr Virus. BMC Infect Dis. 2006;6:15. doi:10.1186/1471-2334-6-15.; Wang LW, Wang Z, Ersing I, et al. Epstein-Barr virus subverts mevalonate and fatty acid pathways to promote infected B-cell proliferation and survival. PLoS Pathog. 2019;15(9):e1008030. Published 2019 Sep 13. doi:10.1371/journal.ppat.1008030
^[19] Maruyama T, Maruyama N, Higuchi T, et al. Efficacy of L-carnitine supplementation for improving lean body mass and physical function in patients on hemodialysis: a randomized controlled trial. Eur J Clin Nutr. 2019;73(2):293-301. doi:10.1038/s41430-018-0348-y; An JH, Kim YJ, Kim KJ, et al. L-carnitine supplementation for the management of fatigue in patients with hypothyroidism on levothyroxine treatment: a randomized, double-blind, placebo-controlled trial. Endocr J. 2016 Oct 29;63(10):885-895. Epub 2016 Jul 16. https://www.researchgate.net/publication/7933618_Muscle_carnitine_in_hypo -_and_hyperthyroidism; Benvenga S, Ruggeri RM, Russo A, Lapa D, Campenni A, Trimarchi F. Usefulness of L-carnitine, a naturally occurring peripheral antagonist of thyroid hormone action, in iatrogenic hyperthyroidism: a randomized, double-blind, placebo-controlled clinical trial. J Clin Endocrinol Metab. 2001 Aug;86(8):3579-94.
^[20] Benvenga S, Feldt-Rasmussen U, Bonofiglio D, et al. Nutraceutical supplements in the thyroid setting: health benefits beyond basic nutrition. Nutrients. 2019 Sep 13;11(9). pii: E2214.; Benvenga S, Ruggeri RM, Russo A, Lapa D, Campenni A, Trimarchi F. Usefulness of L-carnitine, a naturally occurring peripheral antagonist of thyroid hormone action, in iatrogenic hyperthyroidism: a randomized, double-blind, placebo-controlled clinical trial. J Clin Endocrinol Metab. 2001 Aug;86(8):3579-94.
^[21] Benvenga S, Ruggeri RM, Russo A, Lapa D, Campenni A, Trimarchi F. Usefulness of L-carnitine, a naturally occurring peripheral antagonist of thyroid hormone action, in iatrogenic hyperthyroidism: a randomized, double-blind, placebo-controlled clinical trial. J Clin Endocrinol Metab. 2001 Aug;86(8):3579-94.
^[22] Benvenga S, Feldt-Rasmussen U, Bonofiglio D, et al. Nutraceutical supplements in the thyroid setting: health benefits beyond basic nutrition. Nutrients. 2019 Sep 13;11(9). pii: E2214.; An JH, Kim YJ, Kim KJ, et al. L-carnitine supplementation for the management of fatigue in patients with hypothyroidism on levothyroxine treatment: a randomized, double-blind, placebo-controlled trial. Endocr J. 2016 Oct 29;63(10):885-895. Epub 2016 Jul 16. https://www.researchgate.net/publication/7933618_Muscle_ carnitine _in_ hypo-_and_hyperthyroidism
^[23]An JH, Kim YJ, Kim KJ, et al. L-carnitine supplementation for the management of fatigue in patients with hypothyroidism on levothyroxine treatment: a randomized, double-blind, placebo-controlled trial. Endocr J. 2016 Oct 29;63(10):885-895. Epub 2016 Jul 16. https://www.researchgate.net/publication/7933618_ Muscle_carnitine_in_hypo-_and_hyperthyroidism
^[24] Moncayo R, Moncayo H. Applying a systems approach to thyroid physiology: Looking at the whole with a mitochondrial perspective instead of judging single TSH values or why we should know more about mitochondria to understand metabolism. BBA Clin. 2017 Apr 4;7:127-140.
^[25] Fariduddin MM, Bansal N. Hypothyroid Myopathy. [Updated 2019 May 5]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2019 Jan-. Available from: https://www.ncbi.nlm.nih.gov/ books/NBK519513/
^[26] Benvenga S, Feldt-Rasmussen U, Bonofiglio D, et al. Nutraceutical supplements in the thyroid setting: health benefits beyond basic nutrition. Nutrients. 2019 Sep 13;11(9). pii: E2214.; An JH, Kim YJ, Kim KJ, et al. L-carnitine supplementation for the management of fatigue in patients with hypothyroidism on levothyroxine treatment: a randomized, double-blind, placebo-controlled trial. Endocr J. 2016 Oct 29;63(10):885-895. Epub 2016 Jul 16. https://www.researchgate.net/publication/7933618_Muscle_ carnitine_in_hypo-_and_hyperthyroidism; Benvenga S, Ruggeri RM, Russo A, Lapa D, Campenni A, Trimarchi F. Usefulness of L-carnitine, a naturally occurring peripheral antagonist of thyroid hormone action, in iatrogenic hyperthyroidism: a randomized, double-blind, placebo-controlled clinical trial. J Clin Endocrinol Metab. 2001 Aug;86(8):3579-94.
^[27] Fariduddin MM, Bansal N. Hypothyroid Myopathy. [Updated 2019 May 5]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2019 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK519513/
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^[29] Maruyama T, Maruyama N, Higuchi T, et al. Efficacy of L-carnitine supplementation for improving lean body mass and physical function in patients on hemodialysis: a randomized controlled trial. Eur J Clin Nutr. 2019;73(2):293-301. doi:10.1038/s41430-018-0348-y
^[30] Vondra K, Vrbikova J, Dvorakova K. Thyroid gland diseases in adult patients with diabetes mellitus. Minerva Endocrinol. 2005;30(4):217-236.
^[31] Bene J, Hadzsiev K, Melegh B. Role of carnitine and its derivatives in the development and management of type 2 diabetes. Nutr Diabetes. 2018;8(1):8. Published 2018 Mar 7. doi:10.1038/s41387-018-0017-1.
^[32] Ibid
^[33] Ibid
^[34] Weaver LT, Rosenthal SR, Gladstone W, Winter HS. Carnitine deficiency: a possible cause of gastrointestinal dysmotility. Acta Paediatr. 1992;81(1):79-81. doi:10.1111/j.1651-2227.1992.tb12085.x
^[35] Murata S, Inoue K, Aomatsu T, Yoden A, Tamai H. Supplementation with carnitine reduces the severity of constipation: a retrospective study of patients with severe motor and intellectual disabilities. J Clin Biochem Nutr. 2017;60(2):121–124; Irie J, Kanno Y, Kikuchi R, et al. L-Carnitine improves gastrointestinal disorders and altered the intestinal microbiota in hemodialysis patients. Biosci Microbiota Food Health. 2017;36(1):11-16.
^[36] Murata S, Inoue K, Aomatsu T, Yoden A, Tamai H. Supplementation with carnitine reduces the severity of constipation: a retrospective study of patients with severe motor and intellectual disabilities. J Clin Biochem Nutr. 2017;60(2):121–124
^[37] Irie J, Kanno Y, Kikuchi R, et al. L-Carnitine improves gastrointestinal disorders and altered the intestinal microbiota in hemodialysis patients. Biosci Microbiota Food Health. 2017;36(1):11-16.
^[38] Fasano A. Leaky gut and autoimmune diseases. Clin Rev Allergy Immunol. 2012;42(1):71-78. doi:10.1007/s12016-011-8291-x
^[39] Karlsson F, Tremaroli V, Nielsen J, Bäckhed F. Assessing the human gut microbiota in metabolic diseases. Diabetes. 2013 Oct;62(10):3341-9.; Fröhlich E, Wahl R. Microbiota and thyroid interaction in health and disease. Trends Endocrinol Metab. 2019 Aug;30(8):479-490.
^[40] Kępka A, Ochocińska A, Chojnowska S, et al. Potential Role of L-Carnitine in Autism Spectrum Disorder. J Clin Med. 2021;10(6):1202. Published 2021 Mar 13. doi:10.3390/jcm10061202
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^[46] Kitano Y, Hashimoto S, Matsumoto H, et al. Oral administration of l-carnitine improves the clinical outcome of fertility in patients with IVF treatment. Gynecol Endocrinol. 2018;34(8):684-688. doi:10.1080/09513590.2018.1431769
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Note: Originally published September 17, 2021, this article has been revised and updated for accuracy and thoroughness.